Piezoresistive foot pressure measurement method and apparatus

ABSTRACT

A method and apparatus (68, 40) for measuring pressures exerted on 6 human feet or horses&#39; hooves comprises a rectangular array of piezoresistive force sensors encapsulated in a thin polymer package (40) that is inserted into a shoe, or incorporated into a sock that may be pulled over a foot or hoof. The preferred embodiment employs novel piezoresistive normal force or pressure sensing elements (36) which include a polymer fabric mesh impregnated with conductive particles suspended in an elastomeric vehicle, preferably silicone rubber. The piezoresistive mesh layer (33) is sandwiched between an array of row (34) and column (31) conductor strip laminations, preferably made of a nylon mesh impregnated with printed metallic paths. In a variation (100) of the basic embodiment, each normal force sensor element (30) is bordered by laterally and longitudinally disposed pairs (80) of shear force sensor elements, each of the latter comprising a pair of adjacent resilient piezoresistive pads (83) that have longitudinally contacting lateral surfaces. The pads are slidably movable, and when urged into more or less intimate contact in response to shear forces directed normal to their tangent contact plane, the electrical resistance between the pads varies in a predetermined way as a function of the shear forces.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates to methods and apparatus for measuringpressures exerted on the feet of standing humans or animals such ashorses. More particularly, the invention relates to a method andapparatus for providing a two-dimensional map of pressures exerted onthe bottom of a human foot by a shoe, for example, or on the hoof of ananimal, particularly, a horse.

B. Description of Background Art

People who must be on their feet for long periods of time, whetherstanding or walking, are well aware of the discomfort and fatigue thatmay be brought on by reaction pressures exerted on the bottoms of thefeet by the ground or other surface supporting the weight of the person.Accordingly, substantial efforts have been exerted by manufacturers ofshoes, ski boots and other footwear, in an effort to more uniformlydistribute the pressures exerted by footwear on the feet of the wearer.In conjunction with these efforts, a variety of devices for measuringthe forces applied to the foot by footwear have been disclosed in thefollowing United States patents:

Levin et al., U.S. Pat. No. 4,121,453, Oct. 24, 1978, Foot ForceTransducer, which discloses an apparatus for measuring foot forcesduring walking that uses a specially configured spring seated in atransducer plate to transmit static and dynamic forces on the footduring walking to strain gauges mounted on the transducer plate, whichin turn, may be monitored and recorded for diagnostic purposes,particularly to aid in treating patients with lower extremitiesdysfunction.

Confer, U.S. Pat. No. 4,745,930, May 24, 1988, Force Sensing Insole ForElectro-Goniometer, which discloses a force sensing insole that isadapted to be used in association with an electro-goniometer foranalyzing the gait of a patient. The insole includes a body membercomposed of three overlying sheets of thin plastic material which arebonded together, with the intermediate sheet having cut-outs in each ofthe heel, ball and tow portions so as to define three separate internalchambers. A contact switch is positioned in each of the open chambers,and which comprises a plurality of parallel fingers formed of conductiveink on the inwardly facing surface of one of the outer sheets, and anarea of conductive material on the inwardly facing surface of the outersheet. The body member includes a laterally extending flexible strip,and which is adapted to flex and extend outwardly from the wearer'sshoe. Also, lines of conductive ink are provided in the body memberwhich extend from each of the contact switches to a terminal positionedat the end of the strip. In the preferred embodiment, switch closuresare input to a radio frequency transmitter strapped to the waist of asubject, a remote receiver being used to monitor switch closures.

Franks, U.S. Pat. No. 4,858,621, Aug. 22, 1989, Foot PressureMeasurement System, which discloses a foot pressure measurement systemin which pressure measurements are obtained from the variation of lightoutput from an illuminated glass or transparent plate. A reflectivematerial on the top surface of the plate causes an increase in lightintensity escaping from the plate when pressure is applied to thereflective material. The accuracy and resolution of the pressuremeasurements are improved by obtaining a reference measurement of thebackground light intensity and distribution before pressure is appliedand subsequently subtracting this background light from the lightpatterns produced when pressure is applied. The reflectancecharacteristics of the system are improved by using a photographic paperas the reflective material.

Seitz, U.S. Pat. No. 4,862,743, Sep. 5, 1989, Device For Measuring TheAreal Distribution of Compressive Forces, which discloses a device formeasuring the areal distribution of compressive forces which actsubstantially vertically with respect to a deformable measuring surface.A matrix arrangement of force sensors is provided, each of which isformed as a capacitance at crossings of substantially perpendicularconductor paths. The conductor paths are fixed on the opposed surfacesof an elastically deformable area-type dielectric and adapted to beconnected by conductive elements to evaluator electronics. The conductorpaths are printed on plastic substrate films.

Podoloff et al., U.S. Pat. No. 5,033,291, Jul. 23, 1991, FlexibleTactile Sensor For Measuring Foot Pressure Distributions And ForGaskets, which discloses a force and pressure sensor having two sets ofparallel electrodes which are positioned facing one another and arrangedso that electrodes of one set cross the electrodes of the second set atan angle to create a plurality of electrode intersections.Pressure-sensitive resistive material lies between the electrodes ateach intersection. An adhesive layer is applied to at least one of theelectrode sets in areas between electrode intersections to secure thefirst and second electrode sets in facing relationship, the adhesivelayer preferably being applied in a pattern which provides passageswhere the adhesive layer does not exist to allow air to escape frominterior areas of the electrode set. The thickness of the adhesive layermay be adjusted to permit preloading or to provide a threshold level forthe sensor. In order to permit electrodes of the electrode set to betrimmed around their periphery, electrical contact to each electrode ofthe electrode sets is made intermediate the ends of the electrodes. Thisis accomplished by providing an insulating layer over the rear of eachelectrode set having holes therein at the desired intersection pointsand having a plurality of connecting conductors on the back of theinsulating sheet, one for each electrode, which make contact with thecorresponding electrode through the hole in the insulating sheet.

Fullen et al., U.S. Pat. No. 5,323,650, Jun. 28, 1994, System ForContinuously Measuring Forces Applied To The Foot, which discloses aself-contained system for measuring forces applied to the foot of a userthat includes a force sensor array positioned within the user's shoebetween the foot and the inner sole of the shoe, the force sensor arrayincluding a multiplicity of individual force sensors arranged in ahexagonal pattern that covers the entire area of contact between thesole of the user's foot and the inner sole of the shoe, an electroniccircuit module removably attached to the side of the shoe, and a flatinterconnecting cable for electrically coupling the force sensor arrayto the electronic circuit module. The electronic circuit module includesa central processing unit, read-only memory, random access memory, andscanning circuitry for electronically continuously scanning the forcesensor array to obtain information indicative of an instantaneous forcesensed by each one of the multiplicity of individual force sensors ofthe force sensor array, for processing that information to obtain forcedata, and for storing the force data in the random access memory. Anannunciator audibly signals the user when a force on the foot greaterthan a predetermined threshold force is sensed.

In addition to the aforementioned references, the following UnitedStates patents disclose devices generally adapted to the measurement ofpressures exerted on body parts:

Bourland et al., U.S. Pat. No. 5,010,772, Apr. 30, 1991, PressureMapping System With Capacitive Measuring Pad, which discloses acapacitive measuring pad for measuring the pressures exerted by variousportions of a patient's body on a mattress. The pad is constructed oftransverse conductive strips separated by a compressible insulator toform a matrix of pressure sensitive capacitive nodes. The nodes arerepetitively scanned in sequence by a microcomputer to measure theirrespective capacitances, from which measurements a pressure map is thenderived. The resulting pressure map may be displayed on a color graphicsmonitor with different colors representing different pressures. Nodecapacitance is found by measuring the response of the node to a drivingsignal of a known voltage. This measurement is accomplished byconnecting one of the node's transverse conductive strips to a senseamplifier. In order to isolate the node of interest from the influenceof surrounding nodes, all of the conductive strips except the twointersecting the selected node are connected to ground. Furthermore, theinput impedance to ground of the sense amplifier is made negligiblysmall with respect to the other system impedance. In this way, only theconductive strip connected to the driving source has a voltage impressedon it, and the conductive strips of all other nodes in the system aremaintained at ground potential, thus allowing an accurate measurement ofthe one capacitance.

Tamori, U.S. Pat. No. 5,079,949, Jan. 14, 1992, Surface PressureDistribution Detecting Element, which discloses a detecting element forsensing surface pressure distributions comprising a substantially rigidinsulating substrate, a plurality of scanning row electrodes, formed bymetal deposition on said substrate, etched to form a pattern ofsubstantially parallel electrodes which are spaced apart and orientedalong a first axis, a thin resistive film, deposited on said substrate,having a resistance which varies as a function of contact area, asubstantially resilient deformable surface layer, a plurality ofscanning column electrodes, formed by metal deposition on said surfacelayer, etched to form a pattern of substantially parallel columnelectrodes which are spaced apart, said surface layer being bonded tosaid substrate by an anisotropic adhesive so that said column electrodesare oriented along a second axis which is perpendicular to said firstaxis, said surface layer transmitting pressure distribution to said rowelectrodes, resistive film, and column electrodes to form a matrix ofvariable contact resistances to provide analog information relating tothe distribution of surface pressure applied to said surface layer.

Rincoe et al., U.S. Pat. No. 5,253,656, Oct. 19, 1993, Apparatus AndMethod For Monitoring Contact Pressure Between Body Parts And ContactSurfaces, which discloses an apparatus and method for monitoringpressure between the surface of a body part and a contact surfaceemploying a plurality of pressure sensors disposed in a matrix arraybetween the contact surface and the body part. The sensors produceanalog force signals proportional to pressure, and a monitor receivesthe analog signals and produces output signals, preferably digital,having pressure data corresponding to the pressure at each sensor. Acomputer processor receives the output signals from the monitor tocreate a force profile for the sensor array. The sensors may be scannedas a read event in variety of manners, including periodic continuous andtriggered scanning. Where triggered scanning is desired, one or moreswitches act to initiate a read event. This monitoring apparatus andmethod is used, for example, to fit prosthetics, to monitor bed-riddenand wheelchair-bound patients, to reduce paid and sores caused by unevendistribution of pressure and to monitor pressure between a cast and aperson. The sensors may be mounted on a single sheet or on strips forpositioning along the body, and monitoring is accomplished bymultiplexing and digitizing the analog force signals.

In addition to the references cited above, the present inventordisclosed in U.S. patent application Ser. No. 08/254,918, filed Jun. 6,1994, novel Multi-Directional Piezoresistive Shear And Normal ForceSensors For Hospital Mattresses And Seat Cushions. Although the sensorsdisclosed in the aforementioned application are an important advancementin the field, the required characteristics of foot pressure sensors aresomewhat different from those for hospital mattresses and seat cushions.

In addition to the problem of accurately mapping pressures exerted onhuman feet, a need exists for performing such measurements on the hoovesof animals, particularly horses. Since the substantial weight of a horseis concentrated on relatively small portions of the horse's hooves, itshould be the goal of the farrier who fits horseshoes to hooves to trimthe hoof in a manner causing the weight of the horse to be distributedrelatively uniformly over both those portions of the hoof in contactwith the shoes, and those portions in contact with the ground. Thepresent inventor is unaware of any prior art devices that are intendedfor, or particularly well adapted to, mapping pressures exerted on thehooves of an animal.

OBJECTS OF THE INVENTION

An object of the present invention is to provide an apparatus formeasuring pressures exerted on various portions of the bottom of a footby a shoe, in response to the weight of a body.

Another object of the invention is to provide a two-dimensional pressuresensing array for providing a quantitative two-dimensional map ofpressures exerted on various portions of a foot by a shoe or otherfootwear.

Another object of the invention is to provide a planar piezoresistivepressure sensing array for measuring pressures exerted on variousportions of a foot pressing down on the array.

Another object of the invention is to provide a thin, flexiblepiezoresistive foot pressure sensing array that may be fitted betweenthe upper inner surface of a shoe or other item of footwear, and thelower surface of a foot.

Another object of the invention is to provide a sock containing in thesole surface thereof a thin, flexible array of pressure sensors, thesock being wearable over a foot and providing measurements of pressureexerted on various portions of the bottom of a foot, when the foot isplaced in contact with ground or other supporting surface.

Another object of the invention is to provide a sock adapted to fit overthe hoof of a horse, the sock having in the sole portion thereof a thin,flexible array of pressure sensors, thus adapting the sock to measuringthe pressures exerted on various portions of the bottom of a standinghorse's hoof, and thereby providing data permitting a farrier to trimthe hoof in a manner resulting in more even distribution of pressures onthe horse's hooves.

Various other objects and advantages of the present invention, and itsmost novel features, will become apparent to those skilled in the art byperusing the accompanying specification, drawings and claims.

It is to be understood that although the invention disclosed herein isfully capable of achieving the objects and providing the advantagesdescribed, the characteristics of the invention described herein aremerely illustrative of the preferred embodiments. Accordingly, I do notintend that the scope of my exclusive rights and privileges in theinvention be limited to details of the embodiments described. I dointend that equivalents, adaptations and modifications of the inventionreasonably inferable from the description contained herein be includedwithin the scope of the invention as defined by the appended claims.

SUMMARY OF THE INVENTION

Briefly stated, the present invention comprehends apparatus and methodsfor measuring the pressures exerted on the bottoms of feet of standingor running humans and animals, particularly horses.

In a basic embodiment of a pressure measuring apparatus according to thepresent invention, piezoresistive pressure sensors are arranged in atwo-dimensional array having an outline shape similar to that of afootprint, and encapsulated in a thin, flexible polymer sandwich. Eachsensor includes a resiliently deformable piezoresistive pad, theelectrical resistance of which varies inversely with pressure or normalforces exerted on the pad. The piezoresistive sensors are arranged inrows and columns, each of which is electrically conductively connectedto a separate wire at the input end of a flexible electrical cable. Atthe output end of the cable, each wire is connected through amultiplexer to an electrical resistance measuring module such as abridge. In response to electrical control signals, the multiplexermomentarily connects each piezoresistive sensor in the sensor array tothe resistance measuring module, thus producing a sequence of resistancemeasurements proportional to pressures exerted on various portions ofthe foot by the array, and thereby permitting the plotting of atwo-dimensional map of pressures exerted on the foot.

In the preferred embodiment of pressure sensing arrays according to thepresent invention, piezoresistive pads are regions of a piezoresistivemesh layer made by impregnating a fabric mesh, preferably made ofmono-filament strands of a polymer such as polyester or polyethylene,with a piezoresistive material comprising electrically conductiveparticles, such as carbon black, suspended in an insulating elastomericvehicle, such as silicone rubber. The piezoresistive mesh layer issandwiched between a pair of thin polymeric conductor strip laminations,preferably made of nylon. Inner facing surfaces of the two conductorstrip laminations have formed thereon adjacent rows of spaced apart rowand column conductors, respectively. Peripheral contacting surfaces ofthe conductor strip laminations are heat sealed or otherwise bonded toencapsulate the piezoresistive mesh layer, thereby forming a thin, flat,flexible laminated sensor array. Each region of piezoresistive materialsandwiched between a row conductor and a column conductor comprises anindividual normal force or pressure sensor in a rectangular array ofsensors.

In a variation of the basic embodiment of a sensor array according tothe present invention, each normal force sensor element constructed asdescribed above is bordered by laterally and longitudinally disposedpairs of shear force sensor elements. The novel shear force sensoraccording to the present invention comprises a pair of adjacentresilient piezoresistive pads that have longitudinally contactinglateral surfaces. The pads are slidably movable, and when the pads areurged into more or less intimate contact in response to shear forcesdirected normal to their tangent contact plane, the electricalresistance between the pads varies in a predetermined way as a functionof the shear forces. The shear force sensors in the pair laterallyadjacent to a normal force sensor preferably have their sensitive axeslaterally disposed, while the shear force sensor elements in thelongitudinally disposed pair adjacent to a normal force sensor havetheir sensitive axes longitudinally disposed. This arrangement permitsmeasurement of shear forces in two perpendicular directions in the planeof the sensor array.

In the preferred embodiment of the shear force sensor elementsalternating with normal force sensors according to the presentinvention, each element is fabricated by forming mesh impregnatedregions of piezoresistive material that are laterally or longitudinallyseparated, and in tangential contact along longitudinally or laterallydisposed contact zones, respectively.

In another embodiment of the invention, a sock is made of concentricflexible fabric tubes comprising row conductive strips, columnconductive strips and piezoresistive normal force and/or shear forcesensor elements fabricated similarly to the corresponding parts of thenovel planar sensor arrays according to the present invention. Thusconstructed, the sock may be fitted over the foot of a person, or hoofof a horse, and measurements made of forces exerted on the foot or hoof,using the force sensing elements contained in the sock.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an upper perspective view of a normal force sensor elementaccording to the present invention.

FIG. 2 is a first transverse sectional view of the sensor element ofFIG. 1, taken along line 2--2.

FIG. 3 is a second transverse sectional view of the sensor element ofFIG. 1, taken along line 3--3.

FIG. 4 is a lower plan-view of the sensor element of FIG. 1.

FIG. 5A is a graph of resistance versus normal force or pressure for thesensor element of FIG. 1.

FIG. 5B is a graph of resistance versus shear force for the sensorelement of FIG. 15.

FIG. 6 is a fragmentary upper perspective view of a rectangular array ofnormal force sensors of the type shown in FIG. 1.

FIG. 7A is an upper plan-view of a normal force sensor array of the typeshown in FIG. 6, the array being adapted for measuring normal forcesexerted on a human foot.

FIG. 7B is a lower plan-view of the sensor array of FIG. 7A.

FIG. 7C is a lower plan-view of the upper, column lamination of thearray of FIG. 7A.

FIG. 7D is an upper plan-view of the lower, row lamination of the arrayof FIG. 7A.

FIG. 7E is an upper plan view of a row lead-out lamination used to makeelectrical connections to the row lamination of FIG. 7D.

FIG. 7F is a fragmentary, magnified view of a conductive mesh fabricused in an alternate construction of the array shown in FIG. 7A.

FIG. 7G is a lower plan-view of a lower, row lamination employing thefabric shown in FIG. 7E.

FIG. 7H is a plan-view of a piezoresistive lamination comprising part ofthe sensor array of FIG. 7A.

FIG. 7I is a fragmentary upper plan view of the lead-out lamination ofFIG. 7E.

FIG. 8 is a transverse sectional view of the sensor array of FIG. 7A,taken along line 8--8.

FIG. 9 is a longitudinal sectional view of the sensor array of FIG. 7A,taken along line 9--9.

FIG. 10 is an expanded side sectional view of the sensor array of FIG.7A, showing the array bent to fit in a shoe.

FIG. 11 is a rear elevation view of the sensor array of FIG. 7A, inwhich upper and lower lead-out laminations thereof are folded away fromone another.

FIG. 11A is a transverse sectional view of a lower lead-out laminationof FIG. 11, taken along line 11A--11A.

FIG. 12 is an exploded plan-view of an alternate embodiment of a normalforce sensor array similar to the one shown in FIG. 7A, in which FIGS.12A-12E illustrate the lowermost, intermediate, and uppermostlaminations comprising the sensor array.

FIG. 13 is an exploded plan-view of a variation of the normal forcesensor array shown in FIG. 12, in which FIGS. 13A-13E illustrate thelowermost, intermediate, and uppermost laminations comprising the sensorarray.

FIG. 14 is a partially diagrammatic block diagram of the sensor array ofFIG. 7A, showing the array interconnected with processing and displaycircuitry.

FIG. 15 is an upper perspective view of a shear force sensor elementaccording to the present invention.

FIG. 16 is a first transverse sectional view of the sensor element ofFIG. 15, taken along line 16--16.

FIG. 17 is a second transverse sectional view of the sensor element ofFIG. 15, taken along line 17--17.

FIG. 18 is a lower plan-view of the sensor element of FIG. 15.

FIG. 18A is a fragmentary, magnified view of a piezoresistive padcomprising part of the shear force sensor element of FIG. 15, the padbeing fabricated from a mesh fabric.

FIG. 18B is an upper plan-view of a rectangular array of shear forcesensors of the type shown in FIG. 15.

FIG. 19 is a fragmentary exploded view of a sensor array comprised ofnormal force sensors of the type shown in FIG. 1, alternating with shearforce sensors of the type shown in FIG. 15, and showing a portion of anupper lamination thereof peeled away to reveal the sensors.

FIG. 20A is a schematic diagram showing the relative orientation ofsensors comprising the array of FIG. 19.

FIG. 20B is a fragmentary transverse sectional view of the array of FIG.19, taken along line 20B--20B.

FIG. 20C is a fragmentary lower plan-view of the sensor array of FIG.19.

FIG. 20D is an upper plan-view of the array of FIG. 19.

FIG. 20E is a lower plan-view of the array of FIG. 19.

FIG. 21 is an exploded upper perspective view of an array of combined(stacked) shear and normal sensor elements according to the presentinvention.

FIG. 24 is an upper perspective view of a normal force sensor arraycomprising normal force sensors of the type shown in FIG. 1, the arraybeing adapted for measuring normal forces exerted on the hoof of ahorse.

FIG. 25A is a lower plan-view of the sensor array of FIG. 23.

FIG. 25B is a lower plan-view of the upper, column lamination of thearray of FIG. 23.

FIG. 26 is an upper perspective view of another sensor array adapted formeasuring shear forces as well as normal forces exerted on the hoof of ahorse, the array comprising normal force sensors of the type shown inFIG. 1, alternating with shear force sensors of the type shown in FIG.15.

FIG. 27 is a perspective view of a sock incorporating force sensorsaccording to the present invention.

FIG. 28 is a perspective view of an inner, column conductor tubecomprising part of the sock shown in FIG. 27.

FIG. 29 is a longitudinal sectional view of the sock shown in FIG. 27.

FIG. 30 is a view similar to that of FIG. 29, but showing the sock in afolded position.

FIG. 31 is a partly dissected view of the inner, column conductor tubeof FIG. 28, showing the tube cut longitudinally and folded flat.

FIG. 32 is a cut and folded-flat view of an outer, row conductor tubecomprising part of the sock shown in FIG. 27.

FIG. 33 is a fragmentary perspective view of a piezoresistive tubecomprising part of the sock of FIG. 27.

FIGS. 34A and 34E show an upper plan view of the upper lamination of analternate embodiment of the normal force sensor shown in FIG. 20D. FIGS.34B-34D are upper plan views of first, second and third laminations,respectively, of the sensor of FIG. 34A.

FIG. 35 is an upper plan view of the sensor of FIGS. 34A-34E.

FIG. 36 is an upper perspective view of another modification of theshear and normal force sensor of FIG. 20B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 1-33, piezoresistive foot/hoof pressuremeasurement apparatus and methods according to the present invention areshown.

Referring first to FIGS. 1-4, a basic embodiment of a piezoresistivenormal force sensor element usable to measure foot pressure is shown. Asshown in FIGS. 1-4, normal force sensor element 30 includes a first,elongated rectangularly-shaped electrically conductive strip 31 made ofa thin, flexible, electrically conductive fabric, such as Flectron brandnickel/copper plated woven nylon mesh fabric made by Monsanto, TheChemical Group, 800 N. Lindberg, St. Louis, Mo. Normal force sensorelement 30 also includes a second conductive strip 32 disposed in aplane parallel to first conductive sheet 31. Conductive strip 32 isspaced apart from strip 31 in a direction normal or perpendicular tostrip 31. As shown in FIGS. 1-4, conductive sheet 32 is located abovestrip 31, with its longitudinal axis oriented in a first, X direction,while lower conductive sheet 31 is oriented perpendicularly to thelongitudinal axis of the upper sheet in a Y direction. Otherorientations of the upper and lower conductive strips are of coursepossible. Whatever the orientation of conductive strips 31 and 32,sensor element 30 includes a piezoresistive layer 33 sandwiched betweenthe conductive strips. The construction details of piezoresistive layer33 will now be described.

Referring now to FIG. 4, piezoresistive layer 33 of sensor 30 may beseen to preferably include a supporting matrix made of thin, open meshfabric sheet 34. Fabric sheet 34, which is preferably electricallynon-conductive, is preferably woven from monofilament strands of apolymer such as polyethylene or polyester. In an exemplary embodiment ofthe invention, the present inventor has found that a 300 mesh fabricsheet made of 0.002 inch diameter monofilament strands of polyesterproved to be a satisfactory material for fabric sheet 34.

Piezoresistive layer 33 of normal force sensor element 30 is fabricatedby impregnating mesh fabric sheet 34 with a resiliently deformable,partially conductive substance 35 that has an electrical resistanceinversely proportional to normal forces or pressures exerted on thelayer, a property which may be referred to as volume or bulkpiezoresistivity. As will become apparent from the ensuing description,partially conductive substance is defined herein as finely dividedparticles of an electrically conductive material. According to thepresent invention, mesh sheet 34 is impregnated with piezoresistivesubstance 35, the mesh providing a durable and dimensionally stablesupport matrix for piezoresistive substance 35. The present inventor hasfound that a suitable substance 35 for impregnating mesh 34, thusforming piezoresistive layer 33, is an ink composed of about 50% milledcarbon black having a grain size of 2-5 microns, 30% unpolymerizedliquid nitrile rubber, type BUNA N, and 20% ABS plastic resin/hardener,or silicone rubber (e.g., Dow Corning RTV 732) and no hardener.Piezoresistive layer 33 is formed by mixing the aforementionedcomponents thoroughly, applying the mixture to a thickness of about0.004 in. with a spatula, and allowing the mixture to air cure at roomtemperature.

The volume resistivity of piezoresistive layer 33 of normal force sensorelement 30 can be varied to a desired cured value by varying the amountof carbon black added to the liquid rubber, and monitoring theresistivity as those two components are being mixed together. Thepresent inventor has found that a suitable range of volume resistivitiesfor piezoresistive layer 33 is about 5 ohm-cm to 100,000 ohm-cm formeasurement of normal forces in the approximate range of 0-5 psi, and100-300,000 ohm-cm for measurement of forces in the approximate range of5-30 psi. FIG. 5A shows the variation of resistivity versus pressure fora typical sensor element 30.

In example embodiments of normal force sensor element 30, conductivestrips 31 and 32 were cut from a conductive fabric consisting ofnickel/copper coated nylon taffeta and marketed under the brand nameFLECTRON by Monsanto, The Chemical Group, 800 N. Lindberg, St. Louis,Mo. This material has a thickness of 3.8 to 4 mils, is flexible anddrapable, and has a surface resistivity of less than 0.05 ohms persquare. Preferably, each conductive strip 31 and 32 has slits 36 cutperpendicularly inward from opposite longitudinal edges of the strip, toallow stretching of the strip in a direction parallel to itslongitudinal axis. As shown in FIG. 1, slits 36 are located in laterallyspaced apart pairs, one pair being spaced laterally outwards from eachside of piezoresistive layer 33. FIG. 5A illustrates a typical variationof the electrical resistance between lower and electrode conductorstrips 31 and 32 of sensor element 30, as a function of pressure orforce directed normally to the sensor element, i.e., in the Z directionin FIG. 1. FIG. 6 illustrates a planar array 37 of normal force sensorelements 30 in which a plurality of column conductive strips 31 and rowconductive strips 32 form a rectangular matrix of normal force sensorelements. In regions exterior to piezoresistive layers 33 of sensorelements 30, column and row conductive strips 31 and 32 are electricallyisolated from one another, to prevent short circuiting, by means of thincolumn and row insulating strips 38 and 39, respectively. The insulatingstrips may be made of any suitable electrically insulating material,such as nylon. In the preferred embodiment, insulating strips 38 and 39are integral with conductor strips 31 and 32, and formed therefrom byphotoetching conductive plating on the strips where insulating areas arerequired.

FIGS. 7A-11 illustrate a normal force sensor array 40 that isparticularly well adapted for measuring normal forces or pressuresexerted on the bottom surfaces of human feet. Foot pressure sensor array40 employs normal force sensor elements 50 substantially similar inconstruction to the normal force sensor elements 30 shown in FIGS. 1-4and described above, with the sensor elements arrayed in a rectangulararray similar to array 37 shown in FIG. 6. However, foot pressure sensorarray 40 contains additional novel and advantageous structural andfunctional features, as will now be described.

Referring now first to FIGS. 7A and 7C, foot pressure sensor array 40may be seen to include an upper, column conductor strip lamination 41having a substrate 42 made of a thin, flexible sheet of electricallyinsulating material such as woven nylon having a thickness of about 4mils. As may be seen best by referring to FIG. 7A, lamination 41 has theapproximate outline shape of a human foot. As may be seen best byreferring to FIG. 7C, column lamination 41 has formed on the lowersurface thereof a plurality of generally longitudinally disposed,laterally spaced apart column conductive strips 51.

Referring still to FIG. 7C, column conductive strips 51 may be seen tohave a generally rectangular, longitudinally elongated plan-view, andare disposed longitudinally between the toe and heel ends of columnsubstrate 42. Preferably, as shown in FIGS. 7A and 7C, the longitudinaledges of conductive strips 51 curve somewhat to parallel the curvedlongitudinal edges of foot-shaped column substrate 42. As is also shownin FIG. 7C, the width of conductive strips 51 decreases towards the rearof substrate 42, the rear or heel portions of conductive strips 51tapering or "necking" down into thin rectangular "tail" traces 43.Preferably, this necking down is located close to the rear edge of theheel portion of substrate sheet 42, to ensure that sensor elements 50will have sufficient area to be operable as close as possible to theheel edge of sensor array 40.

As shown in FIGS. 7A and 7B, column substrate 42 preferably has anintegral, rectangularly-shaped tab or tongue 44 that protrudes rearwardfrom the heel edge of the substrate sheet. Tongue 44 provides supportfor traces 43, and has a transversely disposed rear edge adapted to beinsertably received by a ribbon cable connector 45, as shown in FIG. 10.

As may be seen best by referring to FIG. 7D, sensor array 40 may be seento include a lower, row conductor strip lamination 46 having a substrate47 made of a sheet of a thin, flexible electrically insulating materialsuch as woven nylon having a thickness of about 4 mils. Row conductorstrip lamination 46 preferably has the same foot-shaped outline ascolumn conductor strip lamina 41. As shown in FIG. 7D, row conductorstrip lamination has formed on the upper surface thereof a plurality ofgenerally laterally disposed, longitudinally spaced apart row conductivestrips 52.

Referring still to FIG. 7D, row conductive strips 52 may be seen to havea generally rectangular, laterally elongated plan-view shape, and aredisposed laterally between inner and outer longitudinal edges ofshoe-shaped row substrate 47.

An individual electrical connection is made to each row of conductorstrips 52 by a separate longitudinally disposed conductive trace 48, asfollows.

Referring now to FIG. 7E, it may be seen that row conductor striplamination 46 is overlain by a thin, longitudinally elongated, lead-outlamination 49, having a thin, flexible insulating substrate 57. As shownin FIG. 7A, lead-out substrate 57 is longitudinally disposed over thecentral longitudinal portion of row conductor strip lamination 46.Substrate 57 is fastened to the upper surface of row conductorlamination 46 by any suitable means, such as adhesive regions 58 betweenthe lower surface of the lead-out substrate and the upper surface of therow conductor lamination.

As shown in FIG. 7E, a plurality of thin, narrow longitudinallyelongated, rectangular-shaped lead-out traces 48 are adhered to theupper surface of lead-out lamination 49. Lead-out traces 48 arelaterally spaced apart from one another, and terminated at the upper ortoe end thereof by a laterally elongated, oval plan-view "flag"appendage 58 that is in electrically conductive contact with thelead-out trace. Flags 58 protrude laterally outwards from a longitudinaledge of lead-out lamination 49, and are longitudinally aligned andspaced apart so as to each be centered over a separate row conductorstrip 52. Each flag conductor 58 is conductively coupled to a separaterow conductor strip 52. In the preferred embodiment, flag conductors 58are adhered to row conductor strips 52 by an electrically conductiveadhesive such as R17012 neoprene-type adhesive, manufactured byStockwell Rubber Company, 4749 Talbut Street, Philadelphia, Pa. 19139.

Referring still to FIG. 7E, lead-out lamination 49 may be seen to havean integrally formed rectangular tongue 59 that protrudes rearward fromthe heel edge of the substrate sheet. Tongue 59 provides support for rowlead-out traces 48, and has a transversely disposed rear edge adapted tobe insertably received by ribbon cable connector 45.

In the embodiment of normal force sensor array 40 employing uppercolumn, conductor lamination 41 and lower, row conductor lamination 46constructed as described above, the lead-out traces 43 and 48 are on thelower and upper facing surfaces of the respective laminations. Thus, therearwardly protruding tongues 44 and 59 supporting the lead-out tracesmust be bent away from one another to prevent the upper and lower tracesfrom contacting one another, and to permit separate electricalconnections to be made to the respective row and column lead-out traces.

In this embodiment of the row, column and lead-out laminations of normalforce sensor array 40, each of the laminations was fabricated asphoto-etched printed circuits from a thin sheet of 0.002 inch thickrip-stop nylon having on one surface thereof a layer of electrolessdeposited copper. The copper-coated sheet was cut to the desiredplan-view shape, as shown in FIGS. 7A and 7B, and the copper layercoated with a photo-sensitive, photo-resist emulsion. Next, aphotographic film positive containing an image of a desired conductorpattern, e.g., column conductive strips, row conductive strips, orlead-out conductive strips or traces was placed in contact with thephoto-sensitized surface, and exposed to light. The exposed substratewas then placed in a solvent bath to remove the non-exposed emulsion,and subsequently placed in an ammonium persulfate bath to etch away thecopper from those regions of the substrate where no conductors pathsappear. The exposed copper conductors on the surface of the substratewere then plated with nickel in an electroless bath, to reduce theoxidation rate of the exposed copper surfaces, and to increase themechanical strength of the conductive strips on the substrate.

In a variation of the photo-etched construction of the column, row andlead-out substrates described above, the copper coated nylon sheet wasovercoated with an electroless deposited layer of nickel prior tophoto-etching. In this case, a ferrous chloride etching solution wasused to remove both copper and nickel from non-conductive portions ofthe substrates. In both cases, it was found that a suitable material forthe substrate was copper coated or copper and nickel coated nylon havinga thickness of about 0.004 inch and a total plating thickness of about0.002 inch.

In the preferred embodiment of normal force sensor array 40, upper andlower laminations 41 and 46 are fabricated by a novel construction thatallows lead-out traces to be on outer, upper and lower surfaces of theupper and lower laminations, respectively, rather than on inner, facingsurfaces. The novel construction eliminates the requirement for separateelectrically conductive feed-throughs required by conventional two-sidedprinted circuits, as will now be described.

According to the present invention, a novel construction of upper andlower laminations 41 and 46 utilizes a substrate made of a materialconsisting of woven mesh of non-conductive strands, in which all of theouter surfaces of each of the strands are plated with a conductivematerial. An example of such a material is Flextron brand nickel/copperplated nylon mesh fabric, part number 3050-226, manufactured byMonsanto.

The aforementioned material has substantial electrical conductivitythrough its thickness dimension as well as in the plane of the fabric.Therefore, as shown in FIGS. 7F and 11A, the material M may haveinsulating paths P etched entirely through the thickness dimension ofthe substrate, thus forming conducting islands, such as A and B, havingidentical upper and lower conductive regions that are in electricalcontact with one another. In this embodiment, as shown in FIG. 7G, rowconnector lead-out lamination 49 is attached to the lower, outer side ofrow conductor strip lamination 46, rather than to the upper, inner sideof the lamination. This arrangement permits inner facing surfaces oflaminations 41 and 46 to have row or column conductive stripselectrically in contact with lead-out strips on the outer surfaces oftongues 44 and 49. With an insulating sheet 44A slid between the innerfacing surfaces of the tongues to prevent short circuiting, as shown inFIG. 10, the two tongues may be inserted into a single edge cardconnector 45 provided with upper and lower connectors contacting upperand lower lead-out traces, respectively.

Referring now to FIGS. 8-11 in addition to FIGS. 7A, 7B, and 7H, normalforce sensor array 40 may be seen to include a piezoresistive lamination63 sandwiched between row conductor lamination 46 and column conductorlamination 41. Piezoresistive lamination 63 can be comprised ofindividual, generally rectangularly-shaped piezoresistive cells similarto piezoresistive layers 33 shown in FIGS. 1-4 and described above.Preferably, however, piezoresistive lamination 63 of sensor array 40 isfabricated as a unitary lamination forming an array of rectangularsensor elements 63A.

Thus, as shown in FIGS. 7H and 8-11, an example piezoresistivelamination 63 of sensor array 40 includes a mesh fabric matrix sheet 64made of a 300 mesh fabric woven from 0.002 inch diameter mono-filamentstrands of polyester fiber and cut to the same plan-view outline shapeas that of column substrate 42 and row substrate sheet 47, but ofslightly smaller size. In an example embodiment tested by the presentinventor, matrix sheet 64 had an outer perimeter that was inset about1/16th inch from the perimeter of column substrate 42 and row substrate47, forming a border 65 of the same width. As will be described below,this perimeter border facilitates encapsulating piezoresistivelamination 63.

In an example embodiment of normal force sensor array 40, mesh fabricmatrix sheet 64 was cut from a 300 mesh fabric sheet made of 0.002 inchdiameter monofilament strands of polyester. Matrix sheet 64 wasimpregnated with an elastomeric piezoresistive substance 66 having avolume resistivity of about 120,000 ohm-cm, a composition of 50% carbonand 50% RTV 732 silicone rubber and a thickness of about 0.002 inch. Thepresent inventor has found that a suitable method for impregnatingmatrix sheet 64 with piezoresistive substance 66 is by spreading thesubstance in the form of a viscous, uncured paste, using a spatulasimilar to those sometimes used in screen printing.

After piezoresistive lamination 63 has been fabricated as describedabove, and piezoresistive substance 66 allowed to cure at about 20° C.for about 4 hours, the lamination is positioned concentrically betweenrow substrate 47 and column substrate 42. The peripheral borders 47B and42B of the row and column substrates are then pressed firmly togetherand thermally fused to one another by the application of heat andpressure, thus hermetically encapsulating piezoresistive lamination 63.So constructed, sensor array 40 is impervious to the effects of moistureand air.

In an alternate construction that seals piezoresistive lamination 63between row and column substrates 47 and 42 against moisture and air,the three laminations are positioned between upper and lower latexrubber sheets 53 and 54, as shown in FIG. 10. Upper and lower latexsheets 53 and 54 have a plan-view shape similar to the plan-view shapesof the substrate, but are slightly larger, providing upper and lowerborder areas, respectively, that may be sealed to each other. In apreferred embodiment of the alternate construction, the latex sheetshave a thickness of about 0.004 inch, and are sealed to each other bystrips of two-sided (double-stick) adhesive tape, such as 3M 950.

In the embodiments of foot pressure sensor array 40, shown in FIGS.7A-7H, the sensor array includes an upper column, conductor striplamination 41 and a lower, row conductor strip lamination 46 having theshape of a left human foot, thus adapting the sensor array to be placedin a shoe to measure pressures exerted on a person's left foot. A mirrorimage sensor array having upper column conductor could be constructedfor measuring pressures on the right foot. However, the present inventorhas found that a single type sensor array may be used for both left andright feet by turning over the array as required.

FIGS. 12A-12E illustrates an alternate embodiment of the foot pressureor normal force sensor array 40 shown in FIGS. 7A-11 and describedabove. The alternate embodiment employs a novel construction using anaperture mask lamination which eliminates the need for conductivelyadhering lead-out lamination trace termination flags to row conductivestrips, as will now be described.

Referring first to FIG. 12A, foot pressure sensor array 300 may be seento include a bottom, column conductor strip lamination 301 comprising ainsulating substrate sheet 302 on which are formed a plurality oflongitudinally disposed, laterally spaced apart column conductive strips311. Column conductive strips 311 terminate at the rear or heel end ofsubstrate 302 in narrowed-down conductive lead-out traces 303 located ona rearwardly protruding, rectangularly-shaped tab or tongue portion 304of substrate sheet 30. Preferably, column conductive strip lamination311 is made from an etched-through fabric sheet, as shown in FIG. 7F anddescribed above. Using this arrangement, the conductive lead-out traces303 are electrically continuous through the thickness dimension of thesubstrate sheet 302, allowing electrical contact to be made to thelead-out traces by lower contacts of a ribbon cable connector 305.

Referring now to FIG. 12B, sensor array 300 may be seen to include apiezoresistive lamination 323. Piezoresistive lamination 323 comprises amesh matrix sheet 324 supporting a piezoresistive substance 326, in aconstruction substantially similar to that of piezoresistive lamination63 described above. Preferably, matrix sheet 324 of piezoresistivelamination 323 has a rearwardly protruding tongue 324A which provideselectrical insulation between column conductive traces 303 below thepiezoresistive lamination, and the lamination above it.

Referring now to FIG. 12C, sensor array 300 may be seen to include a rowconductor strip lamination 306 having an insulating substrate sheet 307made of a thin, flexible, electrically insulating material. Rowconductor strip lamination 306 has formed on a surface thereof aplurality of generally rectangularly shaped, laterally disposed,longitudinally spaced apart row conductive strips 312. Preferably, rowconductive strip lamination 306 is made from an etched-through meshfabric sheet, as shown in FIG. 7F and described above. With thisarrangement, the lower surfaces of row conductive strips 312 may be inelectrical contact with piezoresistive layer 323, while lead-outconnections may be made to the upper surfaces of the conductive stripsprotruding upwards through the mesh substrate sheet 307. The novelmanner of making the aforementioned connections will now be described.

Referring now to FIG. 12D, sensor array 300 may be seen to include anaperture mask lamination 314, made of a thin sheet of flexible,electrically insulating material such as Mylar or nylon. Aperture masklamination 314 consists of a sheet 315 of the above-described material,that has been cut to the same plan-view shape as column and rowlamination substrates 302 and 307. A plurality of laterally elongated,longitudinally aligned and spaced apart apertures 316 is providedthrough the thickness dimension of sheet 315. One such aperture 316 islongitudinally centered on the laterally disposed center line of eachrow conductive strips 312, when aperture mask lamination 314 is stackedon top of row conductor strip lamination 306. Thus located, apertures316 allow electrically conductive contact to be made through insulatingsubstrate 315 to the row conductors 312, by a lead-out laminationlocated above the substrate, as will now be described.

Referring now to FIG. 12E, sensor array 300 may be seen to include alead-out lamination 309, made of a thin substrate sheet 317 ofelectrically insulating material, cut to approximately the sameplan-view shape as aperture mask lamination 309.

A plurality of thin, narrow conductive lead-out traces 308 are providedon a surface of substrate sheet 317. Lead-out traces 308 are laterallyspaced apart from one another, and each is terminated at the upper endthereof by a laterally elongated, oval plan-view "flag" appendage 318that is in electrically conductive contact with the lead-out trace.Flags 318 of lead-out lamination 309 protrude laterally outwards fromcorresponding lead-out traces 308, and are so located as to each bevertically aligned with a separate aperture 316 of aperture masklamination 314, with the lead-out lamination overlying and verticallyaligned with the aperture mask lamination. Therefore, when lead-outlamination 309 is pressed down and adhered to aperture mask lamination314, flags 318 conductively contact row conductor strips 312.

Preferably, lead-out lamination 309 is made from an etched-through meshfabric sheet, as shown in FIG. 7F and described above. With thisarrangement, the lower surfaces of flags 318 may be in conductiveelectrical contact with row conductor strips 312, while lead-out traces308 on the upper surface of lead-out substrate 317 may be electricallycontacted by upper contacts of a ribbon cable connector 305.

Laminations 301, 323, 306, 314, and 315 are stacked vertically andsealed together by 3M double-stick tape to form foot pressure sensorarray 300.

FIGS. 13A-13E illustrate a modification of the alternate embodiment 300of the foot pressure sensor array depicted in FIGS. 12A-12E anddescribed above. Modified foot pressure sensor array 300A shown in FIGS.13A-13E is substantially identical in structure and function to sensorarray 300 shown in FIGS. 12A-12E and described above, except for thespacing between row conductor strips 312A, and corresponding apertures316A and flags 318A. By varying the longitudinal spacing between rowconductor strips 312A, modified foot pressure sensor array 300A may beconstructed so as to have thinner, more densely spaced conductor stripswhere greater sensitivity and spatial resolution are required, such astoe region T and heel region H identified in FIG. 13. Conversely,conductive strips 312 may be wider and less densely spaced in regionssuch as instep region I where less sensitivity and spatial resolutionare required.

FIG. 14 is a partially diagrammatic view of a planar foot pressuremeasuring and mapping apparatus 68 according to the present invention.As shown in FIG. 14, apparatus 68 includes a foot pressure sensor array40 comprised of sensor elements 30 of the type shown in FIG. 1, andsignal processing and display circuitry 70. In the preferred embodiment,foot pressure sensor 40 is connected to signal processor and displaycircuitry 70 by means of a thin, flat, flexible multi-conductor ribboncable 71 that is terminated at one end thereof by ribbon cable connector45. As was described previously and shown in FIG. 10, ribbon cableconnector 45 is adapted to insertably receive rearwardly protrudingtongue 44 of sensor 40, and has individual conductors that frictionallyand electrically conductively contact a separate one of each of the rowand column lead-out conductor traces on the upper and lower surfaces ofthe tongue.

As shown in FIG. 14, interface cable 71 is connected at the other endthereof to an interface module 72 containing means for applying anelectrical sampling signals between a selected column conductive strip51 and a selected row conductor strip 52, to measure the resistancevalue of selected sensor element 30. Resistance is measured by applyinga known voltage across a sensor resistance element, and measuring theresulting current, or applying a known current, and measuring thevoltage drop. Although a d.c. sampling signal may be used for measuringresistances of sensor elements 30, preferably, an a.c. signal is used,to avoid polarizing effects on the sensor elements.

Interface module 72 preferably contains a multiplexer 73, whichsequentially outputs a sequence of mxn signals, each signal beingrepresentative of the resistance value for a particular sensor element30 at the intersection of the mth row conductive strip with the nthcolumn conductive strip. Also in the preferred embodiment, ananalog-to-digital converter (ADC) 74 is connected between an analogresistance measuring circuit 75 and multiplexer 73, which is then of thedigital variety, outputs a serial digital data signal on an RS232 port76. In the preferred embodiment, RS232 port 76 of interface module 72 isconnected to serial data port 77 of a computer 78.

Computer 78 is used to control interface module 72, directing thesequence of addressing sensors 30 in array 40. Computer 78 also performssignal processing functions, using predetermined scaling factors toconvert the resistance values of sensor elements 30 to digital valuesrepresenting normal forces and pressures exerted on the sensors. In thepreferred embodiment, digital numbers representing the pressures on eachof the mxn sensors 30 in array 40 are utilized to produce area maps ofthose pressures, which are displayed on a monitor 79 and stored indigital memory if desired.

FIGS. 15-18 illustrate a shear force sensor element 80 according to thepresent invention. For reasons to be stated later, it would be desirablein some applications to be able to measure shear forces as well asnormal forces or pressures exerted on a foot.

Referring now to FIGS. 15-18, but especially to FIGS. 15 and 16, shearforce sensor element 80 may be seen to include a first elongated,rectangularly-shaped electrically conductive strip 81 made of a thinflexible, electrically conductive fabric, such as Flectron. Shear forcesensor element 80 also includes a second conductive strip 82 spacedapart from strip 81 in a direction normal or perpendicular to strip 81.

Shear force sensor element 80 includes at least one pair of elastomericpiezoresistive pads 83A and 83B located between conductive strips 81 and82. As may be seen best by referring to FIGS. 13 and 14, piezoresistivepads 83A and 83B have surfaces 84A and 84B, respectively, whichtangentially contact one another. Pad 83A is in electrically conductivecontact with lower conductive strip 81, and pad 83B is in electricallyconductive contact with upper conductive strip 82. Thus, when contactingsurfaces 84A and 84B of pads 83A and 83B are urged into more intimatecontact in response to shear forces directed normal to their tangentcontact plane, the electrical resistance between the conductive stripsis reduced, a phenomenon which may be referred to as tangential orsurface piezoresistivity.

As shown in FIG. 16, to electrically isolate lower piezoresistive pad83A, which is conductively coupled to lower conductive strip 81, fromupper conductive strip 82, a thin, flexible insulating sheet 85A ispositioned between that portion of the lower surface of the upperconductive strip that overlies pad 83A, and the upper surface of thepad. In the preferred embodiment, insulating sheet 85A is made of aslippery material such as TEFLON, the lower surface of the sheet therebyfacilitating sliding lateral motion of lower piezoresistive pad 83Arelative to upper conductive strip 82, in response to lateral or shearforces exerted on lower strip 81 relative to upper strip 22. Similarly,a slippery insulating sheet 85B is located between the upper surface oflower conductive strip 81 and upper piezoresistive pad 83B, toelectrically isolate upper piezoresistive pad 83B from lower conductivestrip 81, while permitting slidable motion of the pad with respect tothe strip.

Referring now to FIGS. 15, 16 and 18A, each piezoresistive pad 83 ofshear force sensor element 80 may be seen to preferably include asupporting matrix made of a thin, open mesh fabric sheet 86. Fabricsheet 86, which is preferably electrically non-conductive, is preferablywoven from mono-filament strands of a polymer such as polyethylene orpolyester. In an example embodiment of shear force sensor element 80,fabric sheet 86 was a 300 mesh fabric sheet made of 0.002 inch diametermono-filament strands of polyester.

Mesh fabric sheet 86 is impregnated with a resiliently deformable,partially conductive substance 87 that has an electrical resistanceinversely proportional to compressive forces exerted on the surfaces 84of the pads in response to shear forces on the pads, mesh sheet 86provides a durable and dimensionally stable support matrix forpiezoresistive substance 87. The present inventor has found that asuitable piezoresistive substance 87 for impregnating mesh 86, thusforming piezoresistive pad 83, is an ink composed of about 50% milledcarbon black having a grain size of 205 microns, 30% unpolymerizedliquid nitrile rubber, type BUNA N, and 20% ABS plastic resin/hardener,or silicone rubber (e.g., Dow Corning RTV 732) and no hardener.Piezoresistive pads 83 are formed by mixing the aforementionedcomponents thoroughly, applying the mixture to a thickness of about0.004 in. to matrix mesh 86, using a spatula or flat plastic knife, andallowing the mixture to air cure at room temperature.

The volume resistivity of piezoresistive pad 83 of shear force sensorelement 80 can be varied to a desired cured value by varying the amountof carbon black added to the liquid rubber, and monitoring theresistivity of the liquid mixture as those two components are beingmixed together. The present inventor has found that a suitable range ofvolume resistivities for piezoresistive pad 83 is about 5 ohm-cm to100,000 ohm-cm for measurement of shear forces in the approximate rangeof 0-5 psi, and 100-300,000 ohm-cm for measurement of shear forces inthe approximate range of 5-30 psi.

A suitable material for conductive strips 81 and 82 of shear forcesensor 80 is a conductive fabric consisting of nickel/copper coatedpolyester taffeta and marketed under the brand name FLECTRON byMonsanto, The Chemical Group, 800 N. Lindberg, St. Louis, Mo. Thismaterial has a thickness of 3.8 to 4 mils, is flexible and drapable, andhas a surface resistivity of less than 0.05 ohms per square. Preferably,each conductive strip 81 and 82 has slits cut perpendicularly inwardfrom opposite longitudinal edges of the strip, to allow stretching ofthe strip in a direction parallel to its longitudinal axis. As shown inFIG. 13, slits 88 are located in laterally spaced apart pairs, one pairbeing spaced laterally outwards from each side of a pair of opposedpiezoresistive pads 83. FIG. 5B illustrates a typical variation of theelectrical resistance between lower and electrode conductor strips 81and 82, of sensor element 80, as a function of shear force directednormally to contacting surfaces 84 of piezoresistive pads 83 of thesensor element, i.e., in the X or Y direction in FIG. 15.

FIG. 18B illustrates a planar array 89 of shear force sensor elements 80in which a plurality of column conductive strips 81 and row conductivestrips 82 form a rectangular matrix of shear force sensor elements. Inregions exterior to piezoresistive pads 83 of sensor elements 80, columnand row conductive strips 81 and 82 may be electrically isolated fromone another, to prevent short circuiting, by means of thin column androw insulating strips 90 and 91, respectively. The insulating strips maybe made of any suitable electrically insulating material, such as nylon.Preferably, however, insulating strips 90 and 91 are integral with thenon-conductive fabric substrates of conductive strips 81 and 82. In thiscase, conductive material on the Flectron fabric is stripped away frominsulating areas 90 and 91 by photo-etching using a ferrous chloridesolution.

In the embodiment 89 of a planar shear force sensor array shown in FIG.18B, the sensitive or "S" axis of each shear force sensor element 80 isoriented perpendicularly to the S axis of each of its neighbors. Thisarrangement of shear force sensor array 89 affords a capability formapping shear forces in two orthogonal, X and Y directions parallel tothe plane of the sensors.

After mesh fabric matrix sheets 86 have been impregnated withpiezoresistive substance 87 and the latter allowed to cure, thepiezoresistive pads 83 thus formed are positioned between upper andlower conductive strips 82 and 81. In the preferred embodiment, arectangular array of spaced apart contacting pairs of piezoresistivepads 83A and 83B is formed on a pair of lower and upper fabric matrixsheets 86A and 86B, as for example, by screen printing piezoresistiveink onto the matrix sheets. The matrix sheets are then positionedbetween upper and lower column and row laminations having on the innerfacing surfaces thereof spaced apart column and row electrode conductingstrips, of the type illustrated in FIGS. 7A-7D and described above. Rowand column laminations are then sealed to one another to encapsulatematrix sheets 86A and 86B and pairs of piezoresistive shear forcesensing pads 83A and 83B, in a manner similar to that described abovefor normal force sensor 40.

FIGS. 19-20E illustrate a modification 100 of a foot pressure sensorarray 40 according to the present invention, in which shear force sensorelements similar to elements 80 described above, are interspersed withnormal force sensor elements similar to elements 30 described above.

As may be seen best by referring to FIGS. 19 and 20C, footpressure/shear sensor array 100 includes a rectangular array ofgenerally rectangular plan-view normal force sensor elements 30, inwhich each normal force sensor is bordered on either lateral side by apair of shear force sensor elements 80, with their sensitive axes Saligned in a first horizontal direction, and on either longitudinal sideby a pair of shear force sensors having their sensitive axes S alignedin a second horizontal direction perpendicular to sensitive axes of thefirst pair of shear sensor elements. Aside from the interspersing ofshear force sensor elements 80 with normal force sensor elements 30, theconstruction of foot pressure/shear sensor array 100 is substantiallysimilar to that of foot pressure sensor array 40. Thus, sensor array 100has elements numbered 101-119 that are exactly analogous in structureand function to elements 41-59 of the pressure sensor array 40.Accordingly, a complete understanding of the structure and function ofelements 101-119 may be obtained by referring to the previousdescription of elements 41 through 59.

Thus, as shown in FIG. 20E, foot pressure/shear force sensor 100includes a lower, row conductive strip lamination 106 having rowconductive strips 112. As may be seen best by referring to FIG. 20D,sensor array 100 also includes an upper, column lamination 101 havingcolumn conductive strips 111 that overlie piezoresistive normal forcesensor elements 30, the latter alternating in a rectangular array withshear force sensor elements 80.

In the combined shear/normal force sensor array 100 depicted in FIGS. 19and 20C, normal force sensor elements 30 are preferably fabricated byimpregnating a mesh fabric matrix sheet 34 with square areas ofpiezoresistive material 35, the squares being arranged in paralleldiagonal rows, such as rows 92 in FIG. 19. As shown in FIGS. 19 and 20C,diagonal rows 92 of normal force sensor elements 30 alternate withdiagonal rows 93 of shear force sensor elements 80. As is also shown inFIGS. 19 and 20C, the sensitive axes S of shear force sensor elements 80in each diagonal row alternate between the X and Y directions.

One method of fabricating array 100 of normal force sensors 30alternating with shear force sensors 80 consists of perforating normalforce sensor array matrix sheet 34 with square apertures 120 alignedwith diagonal rows 93 of shear force sensor elements 80. Preferably,apertures 120 are slightly larger than shear sensor elements 80. Withthis arrangement, perforated normal force matrix sheet 34 may bevertically aligned with a pair of matrix sheets 86A and 86B on which areformed the pairs 83A and 83B of piezoresistive pads of shear forcesensor elements 80. Thus configured, normal force matrix mesh sheet 34could be located above or below shear force matrix sheet pair 86A and86B. Preferably, however, normal force matrix mesh sheet 34 is locatedbetween lower and upper shear force matrix sheets 86A and 86B.

FIG. 21 illustrates an array 130 of combined shear/normal force sensorelements according to the present invention. The embodiment of theinvention shown in FIGS. 19 and 20 includes normal force sensor elements140 that are substantially similar in structure and function to normalforce sensor element 30 shown in FIGS. 1-4 and described above, stackedabove or below shear force sensor elements 150 which are substantiallysimilar in structure and function to shear force element 80 shown inFIGS. 16 and 18 and described above. Thus, as shown in FIG. 21, stackedshear/normal force sensor array 130 includes a planar array 130A ofshear force sensor elements 80 which have a common first, lowerlamination 80A having on the upper surface thereof inner column or rowconductive strips 81 and, a second, upper lamination 82A having on thelower surface thereof row or column conductive strips 82. As shown inFIG. 21, each shear force sensor element 80 of array 130A includes apair of elastomeric piezoresistive pads 83A and 83B located betweenconductive strips 81 and 82. Piezoresistive pads 83A and 83B havesurfaces 84A and 84B, respectively, which tangentially contact oneanother. Pad 83A is in electrically conductive contact with lowerconductive strip 81, and pad 83B is in electrically conductive contactwith upper conductive strip 82. Thus, when contacting surfaces 84A and84B of pads 83A and 83B are urged into more intimate contact in responseto shear forces directed normal to their tangent contact plane, theelectrical resistance between the conductive strips is reduced, aphenomenon which may be referred to as tangential or surfacepiezoresistivity. As shown in FIG. 21, shear force sensor element pads83A and 83B preferably are arranged in array 130A so that the tangentplanes of adjacent shear force sensor elements 80 are perpendicular toone another. This arrangement permits measurement resolution of shearforces in any direction parallel to array 130A into two mutuallyorthogonal components.

To electrically isolate lower piezoresistive pads 83A, which areconductively coupled to lower conductive strips 81, from upperconductive strips 82, thin, flexible insulating strips 85A arepositioned between that portion of the lower surface of the upperconductive strip that overlies pads 83A, and the upper surface of thepads. In the preferred embodiment, insulating strips 85A are made of aslippery material such as TEFLON, the lower surface of the sheet therebyfacilitating sliding lateral motion of lower piezoresistive pad 83Arelative to upper conductive strip 82, in response to lateral or shearforces exerted on lower strip 81 relative to upper strip 22. Similarly,slippery insulating strips 85B are located between the upper surface oflower conductive strips 81 and upper piezoresistive pad 83B, toelectrically isolate upper piezoresistive pad 83B from lower conductivestrip 81, while permitting slidable motion of the pads with respect tothe strip. In the preferred embodiment, each piezoresistive pad 83A and83B is fabricated integrally with conductive strip 81 or 82 wasdescribed above with reference to FIGS. 15, 16 and 18A.

Stacked shear/normal force sensor element array 130 also includes normalforce sensor elements 30 which have a common first, lower lamination 31Ahaving on the upper surface thereof column or row conductive strips 31.Lower conductive strips 31 may be adhered to the upper surface of aninsulating sheet positioned over shear force array upper lamination 82A.Alternatively, lamination 82A may be a double-sided printed circuit, thelower surfaces of the insulating sheet having formed thereon tracescomprising the upper, column conductive strips 82 of shear force sensorelements 80, and having formed on the upper surface thereof tracescomprising the lower, row conductive traces 31 of normal force sensorelements 30. However, in the most preferred embodiment, lamination 82Ais fabricated with conductive strips extending through the thicknessdimension of the lamination, according to the novel constructionemploying etched, plated fabric described above. With this arrangement,upper, column conductive strips 82 of shear force sensor elements 80 maybe common with lower column conductive strips 31 of normal force sensorelements 30.

Sensor array 130 also includes an upper lamination 132A having on thelower surface thereof a plurality of column or row conductive strips132, that are disposed perpendicularly to conductive strips 31. Apiezoresistive layer 133 is positioned between column and row conductivestrips 31 and 132, and functions in response to normal forces exertedthereon as has been previously described.

Thus constructed, combined shear/normal force sensor elements 130 can bearranged in a rectangular array similar to that shown in FIGS. 7A-7D.However, in this case, one or two additional lead-out tongues 144A, 144Bmust be brought out from the array, as indicated by the dotted lines inFIG. 7A. The additional lead-out tongues are required to accommodate thetwo additional layers of conductors required for the stackedconfiguration of shear and normal force sensors.

In the arrangement of stacked shear/normal force sensor element 130shown in FIGS. 19 and 20, normal force sensor element 30 is positionedabove shear force sensor element 80. This order could of course bereversed.

FIGS. 24-25A illustrate a normal force sensor array 160 that isparticularly well adapted for measuring normal forces or pressuresexerted on the bottom surfaces of horses' hooves, by horseshoes, forexample. Hoof pressure sensor array 160 employs normal force sensorelements 170 substantially similar in structure and function to thenormal force sensor elements 30 shown in FIGS. 1-4 and described above,with the sensor elements arranged in a rectangular array similar toarray 37 shown in FIG. 6. Also, hoof pressure sensor array 160 issubstantially similar in structure and function to foot pressure sensorarray 40. Thus, hoof pressure sensor array 160 has elements 161-187substantially similar in structure and function to elements 41-67 offoot pressure sensor array. Since the structure and function of thelatter elements were described in detail above, a thorough understandingof the corresponding elements of hoof pressure sensor array 160 may beobtained by referring to that description.

As may be seen by referring to FIGS. 24-25A, some of the constructiondetails of hoof pressure sensor 160 differ somewhat from those of footpressure sensor 40. Thus, as shown in FIGS. 23-24B, the laminationscomprising hoof pressure sensor 160 have in plan-view a shapeapproximating a horse's hoof print rather than a human foot print. Also,the piezoresistive substance 186 used to impregnate mesh fabric matrixsheet 184 differs from piezoresistive material 66 used in foot pressuresensor array 160 by having a higher volume resistivity of about 500,000ohm-cm versus 100,000 ohm-cm, thus resulting in a piezoresistive layer183 that has greater linearity and minimum hysteresis for the largerpressure ranges of 1,000 to 6,000 psi resulting from the larger weightof horses.

It will be recalled that a planar foot pressure measuring and mappingapparatus 68 illustrated in FIG. 12 was described above. That apparatusincludes a foot pressure sensor array 40, which may be replaced by hoofpressure sensor array 160, thus enabling apparatus 68 to measure and maphoof pressures rather than foot pressures.

FIG. 26 is a lower plan-view of a modification 200 of a hoof pressuresensor array 160 according to the present invention, in which shearforce elements similar to elements 80 described above, are interspersedwith normal force sensor elements similar to elements 30 describedabove. Modified hoof pressure/shear sensor array 200 is substantiallysimilar in structure and function to modified foot pressure/shear sensorarray 100 illustrated in FIGS. 17-18B and described above. Thus, hoofpressure/shear force sensor array 200 has elements 201-219 substantiallysimilar in structure and function to elements 101-119 of footpressure/shear force sensor array 100. Since the structure and functionof the latter elements were described in detail above, a thoroughunderstanding of the corresponding elements of hoof pressure/shear forcesensor array 200 may be obtained by referring to that description.

As was described above, stacked, combined shear/normal force sensorelements 130 can be substituted for alternating normal force sensorelements 30 and shear forced elements 80 in foot pressure/shear forcesensor array 100. This substitution could of course also be made in hoofpressure/shear force sensor array 200.

FIGS. 27-33 illustrate a sock 220 that may be fitted with any of thesensor arrays 40, 100, 160, or 200 described above. The construction ofsock 200 is as follows: The sock is made up of three conductive tubularlaminations, an inner tube 221 with longitudinal conductor strips, acenter tube 222 bearing piezoresistive material and an outer tube 223containing lateral or circumferentially disposed conductor strips whichwrap around the sock. A fourth, lead-out layer/strip 224 is provided tomake electrical contact with each of the lateral conductor strips.

In the preferred embodiment of force sensing and mapping sock 220, eachof tubes comprising the sock is made of a mesh fabric material. Thus,inner, column conductor lamination 221, row conductor lamination 223,and row lead-out lamination 224 are preferably made of a conductive meshfabric such as the Flectron material described above.

As shown in FIG. 31, inner column conductor tubular lamination 221comprises a tubular Flectron sock base or matrix 231, having etchedthrough the thickness dimension thereof, longitudinally disposedinsulating paths 232 defining longitudinally disposed, laterally spacedapart column conductors 233 terminating at the opening of the sock inlead-out traces 234.

As shown in FIG. 32, outer, row conductor tubular lamination 223comprises a tubular Flextron sock base or matrix 241 having etchedthrough the thickness dimension thereof circumferentially disposedinsulating paths 242 defining circumferentially disposed, longitudinallyspaced apart row conductors 243.

As shown in FIGS. 29 and 33, piezoresistive tubular lamination 222comprises a tubular sock made of a non-conducting mesh fabricimpregnated with piezoresistive material, in a manner previouslydescribed.

Referring now to FIGS. 27 and 29, force sensing and mapping sock 220 maybe seen to include an outer tubular row lead-out tubular lamination 224.Lead-out tubular lamination 224 is made from Flextron material havingetched through the thickness dimension thereof circumferentially andlongitudinally disposed insulating paths 262 and 263 defining laterallydisposed longitudinally flag appendages 264 connected to longitudinallydisposed lead-out traces 265.

FIGS. 34 and 35 illustrate an alternate embodiment of a force sensorarray according to the present invention, which utilizes a variation ofthe shear force elements previously described.

As shown in FIGS. 34A-34C and 34E, alternate shear force sensor array400 has laminations 401A, 423, 426, and 401B, substantially identical instructure and function to those previously described with reference toFIGS. 12, 20D and 20E. However, in the embodiment 400 of a force sensorarray, shear force sensors 480 are arrayed in a separate layer using thehorizontal conductive elements from a normal force sensor as a firstconductive array on a first side of the shear force sensor elements, anda second layer of vertical conductive elements as a second,perpendicular conductive array for the second side of the shear forcesensor elements.

As shown in FIG. 34D, each shear force sensor element 480 includes apair of mating right-triangularly-shaped piezoresistive pads 483A and483D having mating hypotenuse surfaces 484A and 484B, the two pads thusdefining a square shape. Each shear force sensor element pad 483A, 483Bhas a teflon coating or sheet 485A, and 485B adhered to one sidethereof. The other side of each pad is in electrically conductivecontact with a row or column conductor strip. Shear forces imposed onthe pads 483A and 483B urge the pads into more or less intimate contact,thus varying the electrical resistance between the pads.

With pads 483A and 483B slidably movable towards one another, withoutany pre-load forcing the pads together, sensor element 480 is moresensitive to forces tending to urge the pads into more intimate contactthan to forces tending to separate the pads. This somewhat non-bilateralcharacteristic may also be present in the basic embodiment of shearforce sensor element according to the present invention and describedabove. Thus, in the absence of a pre-load force tending to bias pads483A and 483B together, it is preferable to employ diagonally opposedpairs of sensor elements 480A and 480B as shown in FIG. 34, assuringadequate bilateral sensitivity of the sensor element pad array, as shownin FIG. 35.

In another shear force sensor array embodiment shown in FIG. 36,circularly-shaped, piezoresistive pads 503 are placed on multi-conductorflat cable 500. Spots 502 are bared on (hc flat cable to coincide withplacement of the four circular pads 503 of the shear sensor 499. Thisallows the pads to contact the flat cable and these are adhered to thecable using a conductive adhesive. There are also two additional baredareas which make up the normal force sensor element. One of the centralnormal force elements acts as the common electrical contact and theother is covered with a layer of piezoresistive normal force sensingmaterial 501. A central round aluminum element 504 comes into contactwith the central piezoresistive layer 501, allowing it to act as thenormal force sensing element. Element 504 also tangentially contactspads 503 and serves as the common element for those pads. The tops ofthe four pads 503 are covered with Teflon sheet 505 to reduce frictionwith the plastic cover plate 506. The whole assembly is covered withlatex rubber 507 to ensure a good friction to surrounding surfaces.

What is claimed is:
 1. A device for measuring forces exerted on adiscrete location of a surface, said device comprising at least a firstnormal force sensing element (30), said element containing apiezoresistive material defined as having a hulk electrical resistancethat varies in a predetermined way with normal forces exerted thereon,said piezoresistive material being in the form of a resilient pad (33)sandwiched between a pair of first and second conductor striplaminations comprising thin, flexible insulating sheets having formed onthe inner facing surfaces thereof at least one row (32) and at least onecolumn (31) conductor strip, respectively, said row and column conductorstrips being in electrically conductive contact with opposite sides ofsaid piezoresistive pad, at least one of said resilient pads, said rowand said column conductor strips comprising a woven mesh fabric (34)impregnated with electrically conductive material, whereby theelectrical resistance between a selected row and column conductorintersection defining a particular region normally aligned with saidpads in a predetermined function of the normal force exerted on saidregion.
 2. The device of claim 1 wherein at least one of said row andcolumn conductor strips is further defined as being made of anelectrically conductive, woven fabric that is flexible and drapable. 3.The device of claim 1 wherein at least one of said conductor strips isfurther defined as having formed therein at least one transverselydisposed slit (36) spaced apart from said piezoresistive pad (33), saidslit facilitating longitudinal stretching of said strip.
 4. The deviceof claim 1 further comprising at least one additional one of saidresilient pads (33), each of said first and additional pads being spacedapart and electrically isolated from one another and comprising togethera planar two dimensional array (37) of said force sensing elements. 5.The device of claim 4 wherein said piezoresistive pads are each furtherdefined as comprising an insulating matrix (34) impregnated with apiezoresistive substance (35).
 6. The device of claim 5 wherein saidmatrix (34) is further defined as being a woven mesh fabric.
 7. Thedevice of claim 6 wherein said woven mesh fabric is further defined asbeing flexible and drapable.
 8. The device of claim 4 wherein saidpiezoresistive substance (35) is further defined as comprising asuspension of conductive particles in a resilient material.
 9. Thedevice of claim 8 wherein said resilient material is further defined asbeing an elastomer.
 10. The device of claim 9 wherein said elastomer isfurther defined as being silicon rubber.
 11. The device of claim 8wherein said conductive particles are further defined as being composedof carbon.
 12. The device of claim 4 wherein said row (32) and column(31) conductor strips extend through the thickness dimension of saidfirst and second conductor strip laminations, whereby electrical contactis made with said inner facing row and column conductor strips incontact with said piezoresistive elements by contacting elements on theouter surfaces of said cover sheets.
 13. The device of claim 12 whereinsaid first and second, row and column conductor strip laminations arefurther defined as comprising a conductive fabric sheet consisting of anon-conducting fabric mesh composed of woven strands of non-conductivefibers which are plated on the outer surfaces thereof with a conductivemetallic coating, said coating being etched through the thicknessdimension of said mesh to produce insulating paths (33) definingconductive strips (A,B) that extend through the thickness dimension ofsaid mesh.
 14. A device for measuring shear forces exerted on discretelocations of a surface which the apparatus is placed in contact with,said device comprising a planar two dimensional array of individualshear force sensing elements (80), each of said shear force sensingelements comprising a pair of laterally adjacent piezoresistive pads(83A, 83B) having tangentially contacting peripheral surfaces (84A,84B), the electrical resistance between said pad pair members varying ina predetermined way with shear forces directed perpendicularly to thetangent plane and urging said contacting surfaces of said pad pair intogreater or lesser conductive contact, said pairs of pads beingsandwiched between a pair of first and second conductor striplaminations comprising thin, flexible electrically insulating sheetshaving formed on the inner facing surfaces thereof adjacent rows ofspaced apart row (82) and column (81) conductor strips, respectively,said row and column conductor strips being in electrically conductivecontact with a separate one of each pair of pads, whereby measurement ofthe electrical resistance between the pads of a selected pair of saidpads is measured by applying a voltage between said selected row andcolumn conductor strips, thereby determining shear forces exerted onsaid pad pair.
 15. The device of claim 14 wherein at least one of saidhalves of a pad pair is slidably supported by an electricallynon-conductive sheet (85) on the surface opposite to that surface inelectrically conductive contact with said pad.
 16. The device of claim14 wherein said piezoresistive pads of said shear force sensing elementsare each further defined as comprising an insulating matrix (86)impregnated with a piezoresistive substance (87).
 17. The device ofclaim 16 wherein said piezoresistive substance is further defined ascomprising a suspension of conductive particles in a resilient material.18. The device of claim 17 wherein said resilient material is furtherdefined as being an elastomer.
 19. The device of claim 18 wherein saidelastomer is further defined as being silicone rubber.
 20. The device ofclaim 17 wherein said conductive particles are further defined as beingcomposed of carbon.
 21. The device of claim 14 wherein said row andcolumn conductor strips extend through the thickness dimension of saidfirst and second conductor strip laminations, whereby electrical contactmay be made with said inner facing row and column conductor strips incontact with said piezoresistive pads by contact elements on the outersurfaces of said laminations.
 22. The device of claim 15 wherein saidfirst and second, row and column conductor strip laminations are furtherdefined as comprising a conductive fabric sheet consisting of anon-conducting mesh fabric composed of woven strands of non-conductivefibers which are plated on the outer surfaces thereof with a conductivemetallic coating, said coating being etched through the thicknessdimension of said mesh to produce insulating paths defining conductivestrips that extend through the thickness dimension of said mesh.
 23. Thedevice of claim 1 further adapted for measuring pressures exerted atvarious locations on the bottom of a foot in response to weight placedon the foot and comprising a thin, flexible laminated structurecontaining a plurality of piezoresistive pressure sensing elementsarranged in a planar two-dimensional array, said laminated structurecomprising a first, column conductor strip lamination including asubstrate made of a thin, flexible sheet of electrically insulatingmaterial having formed on a surface thereof a plurality oflongitudinally disposed, laterally spaced apart column conductor strips,a second, piezoresistive lamination comprising a thin substrate matrixsupporting a thin layer of resilient piezoresistive material having anelectrical resistance measured normal to said layer that varies withnormal forces exerted thereon, said piezoresistive layer having a firstplanar surface which is in electrical contact with said column conductorstrips, a third, row conductor strip lamination including a substratemade of a thin, flexible sheet of electrically insulating materialhaving formed on an inner surface thereof a plurality of laterallydisposed, longitudinally spaced apart row conductor strips inelectrically conductive contact with a second planar surface of saidpiezoresistive layer, and means for making electrically conductivecontact with a selected pair of row and column conductor strips wherebythe resistance of a selected piezoresistive element defined by thatportion of said piezoresistive layer between said strips may bemeasured, said resistance being related in a predetermined way topressure exerted on said element.
 24. The device of claim 23 whereinsaid row and column conductor strip laminations are further defined ashaving longitudinally elongated lead-out tongues supporting lead-outtraces in electrically conductive contact with said respective row andcolumn conductor strips, said tongues protruding away from the pressuresensor area defined by said piezoresistive lamination.
 25. The device ofclaim 24 where said lead-out tongues are further defined as beingvertically aligned and splayed vertically apart, thereby allowingseparate edge card connectors to electrically contact separate lead-outtraces on the inner facing surfaces of said tongues.
 26. The device ofclaim 23 wherein at least one of said column and row conductor striplaminations is further defined as comprising a conductive fabric sheetconsisting of a non-conducting fabric mesh composed of woven strands ofnon-conductive fibers which are plated on the outer surfaces thereofwith a conductive metallic coating, said coating being etched throughthe thickness dimension of said mesh to produce insulating pathsdefining conductive strips that extend through the thickness dimensionof said mesh.
 27. The device of claim 23 wherein said column and rowconductor strip laminations are further defined as comprising aconductive fabric sheet consisting of a non-conducting fabric meshcomposed of woven strands of non-conductive fibers which are plated onthe outer surfaces thereof with a conductive metallic coating, saidcoating being etched through the thickness dimension of said mesh toproduce insulating paths (38) defining conductive strips (A,B) thatextend through the thickness dimension of said mesh.
 28. The device ofclaim 27 wherein said column (41) and row (46) conductor striplaminations are further defined as having longitudinally elongatedlead-out tongues (44) supporting lead-out traces (43) in electricallyconductive contact with said respective column and row conductor strips,said lead-out tongues protruding away from the pressure sensing areadefined by said piezoresistive laminations and being vertically alignedin a parallel relationship with an insulating strip between the innersurfaces of said tongues, said lead-out traces being located on theouter surfaces of said tongues.
 29. A device for measuring shear andnormal forces exerted on discrete locations of a surface, said devicecomprising a planar array of at least one shear force sensor element asrecited in claim 14, interspersed with at least one normal force sensingelement (30) containing a piezoresistive material defined as having abulk electrical resistance that varies in a predetermined way withnormal forces exerted thereon, said piezoresistive material being in theform of a resilient pad (33) sandwiched between a pair of first andsecond conductor strip laminations comprising thin, flexible insulatingsheets having formed on the inner facing surfaces thereof at least onerow (32) and at least one column (31) conductor strip, respectively,said row and column conductor strips being in electrically conductivecontact with opposite sides of said piezoresistive pad, at least one ofsaid resilient pads, said row and said column conductor stripscomprising a woven mesh fabric (34) impregnated with electricallyconductive material, whereby the electrical resistance between aselected row and column conductor intersection defining a particularregion normally aligned with said pads is a predetermined function ofthe normal force exerted on said region.
 30. The device of claim 29wherein said normal force sensor element and shear force sensing elementare arranged in a laterally spaced apart disposition relative to oneanother.
 31. The device of claim 29 wherein said normal force sensorelement and said shear force sensor element are arranged in a verticallystacked disposition relative to one another.